After market tach on 92 Seca II

[krifartida]

I am working on this Seca II.
PO has stripped the original cluster, in favor of a vintage CB light bucket and speedo.
Both work 100% and the entire harness is intact and and was wrapped neatly and tucked away.

So - i ordered an El cheapo tach (13K rpm), 3 wire lead unit.

Nice.

Plug in the brown wire to live, black wire to ground, and grey wire to signal/igniter lead.

Start the bike - and nothing.

multimeter Tested both pos and neg leads for 12V and they are good.

What am i missing?

Where/how can i test the signal lead?

Any way to test the tach itself, i have no other bike to do that with at the moment.

Any ideas?